Method of retorting oil shale in situ

ABSTRACT

This invention relates to a process for the recovery of oil from an underground, unmined zone of oil shale. Access is obtained at at least two points in the zone, which can be, for example, in a shallow zone, near the top and bottom of the zone, communication is established between the access means, and at least part of the oil shale zone is fragmented. The heat of retorting is supplied through one of the access means, as by a gas, and the pyrolyzed oil is recovered from the other access means.

United States Patent [56] References Cited UNITED STATES PATENTS [72]Inventor Rex'LEllington Tulsa, Okla.

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mented. The heat of retorting is supplied through one of the accessmeans, as by a gas, and the pyrolyzed oil is recovered from the otheraccess means.

[50] Field AIR METHOD OF RETORTING OIL SHALE IN SITU The recovery of oilfrom oil shale has heretofore generally been accomplished by one of twomethods. The first such method includes mining the oil shale out of theground, crushing and then retorting or pyrolyzing the crushed oil shalein a fixed retorting plant or structure to retort the oil containedtherein. The predominant processes of retorting oil shale are thedownflow and upflow gas combustion retorts processes and the hot pebblesolid-solid heat transfer process. The second such recovery method isthe retorting of the oil shale in situ, or in place, which eliminatesthe need for a retorting plant and its attendant apparatus. Generally,the in situ method has used conventional injection and producing wellsin naturally fractioned zones in the shale body, or the use ofcommunication paths established between the wells by explosive,hydraulic, chemical or electric fractioning means. Recently, nucleardevices have been considered to create a chimney of broken shale withwhich communication could be established for pyrolysis.

The above ground retorting operations employed generally are cumbersomeand expensive, involving large equipment and high operating costs perunit of shale processed. Important factors contributing to theseeconomic burdens have been poor heat heat recovery in the retortingsystem and the expense, equipment and time consumed in mining andcrushing the shale, and in subsequently recovering the products ofretorting. These conditions have led to many efforts to process the oilshale in place to eliminate the expense of a crushing and retortingplant.

Retorting oil shale in situ as shown by the prior art has certaindisadvantages. Operation through wells in naturally fractioned zones hasthe disadvantage that fracture patterns may not be known and theeffective porosity and penneability of the formation may not representdesirable values. In addition, all the oil that is developed may not becarried to the producing well because of it banking up ahead of thedriving gas. In technical terms, the displacement efficiencies and thesweep efficiency may thus be so low as to render the process uneconomic.Also, if the natural fracturing does not expose sufficient surface area,it may not be possible to pass sufficient heat into the shale body todevelop sufficient oil in a given period of time to make the processprofitable.

U.S. Pat. No. 3,342,257 discloses the utilization of nuclear devices tofragment shale to recovery of the hydrocarbons in situ. The chimney may,however, fill with water and require operating at pressures too high tobe profitable. Furthermore, the hazards of such a process are apparent.The broken shale may also be distributed nonuniformly as to size andgive rise to channeling of combustion gases and result in technical andeconomic failure. Massive walls will also have to be left betweensuccessive shots to prevent breakthrough and these will remain largelyunretorted resulting in a waste of natural resources. Furthermore, thismethod cannot be used in shallow or thin beds near outcrops, or nearmine workings.

It is also known that the first oil and gas produced from nuclearchimney retorting may be contaminated with radioactive products and beunuseable. Ground water may be contaminated. Further, nuclear chimneysmay be so tall that the loading of material above retorting zones in thelower part of the chimney may exceed the strength of the oil shale athigh temperatures and cause local collapse with resulting shutoff offlows.

The present invention is a process for breaking up and pyrolyzing oilshale in situ in a wide variety of areas, such as near outcrops, aboveand below mine workings, under close control, thereby eliminating theneed for a crushing plant, conventional materials handling, retortingplant, and spent shale disposal. This invention can also be used in theproduction of raw shale oil underground by the thermal treatment of thesolid carbonaceous material in outcrop zones which may be tooincompetent or too lean for mining. The present invention also createsrelatively small chimneys of broken oil shale for pyrolysis underclosely controlled conditions so that fragmentation is optimized. Thepresent invention also provides for control of the rate of pyrolysis notpossible with current in situ methods by generating and distributingporosity in the body. The present invention also produces raw shale oilunderground by means which do not require transport of a major amount ofthe shale to the surface and do not require construction of a surfaceretorting plant, although such may be desirable for optimum utilization.Further, the present invention provides an inexpensive method ofprocessing essentially in situ zones of oil shale too lean forprofitable recovery by other means.

An object of this invention is to minimize residence times attemperatures above about l,500 F. to minimize solubility of secondaryminerals in order to facilitate their recovery. A further object is tofollow the retorting operation with leaching of the shale ash with wateror specific solutions to leach out and recover mineral values as taughtin copending application Ser. No. 571,649, filed Aug. 10, 1966, now U.S.Pat. No. 3,516,787. Frequently, oil shale contains quartz, dolomite anddawsonite (sodium aluminum carbonate hydroxide). The above applicationdiscloses a method to recover aluminum values from a mixture of thistype without substantial precipitation of SiO,,. 7

The present invention comprises establishing access means at at leasttwo points in a zone of unmined oil shale, establishing communicationbetween these access means through the zone, fragmenting at least partof the oil shale in the zone in the area of the communication to producea porous means of fragmented oil shale, supplying heating means to saidfragmented oil shale through one of said access means to pyrolyze shaleoil in the oil shale and collecting the said shale oil through other ofsaid access means.

The invention will be further illustrated with reference to the appendeddrawings in which:

FIGS. la, lb and 1c are a graphic representation of one embodiment ofthis invention;

FIG. 2 is a representation of another embodiment of this invention usingtwo contiguous zones;

FIG. 3 is a representation of another embodiment of this inventionparticularly applicable to zones of great height.

FIG. la shows a side view of a section of an oil shale zone, generallydesignated as a. Two access means such as tunnels or drifts l and 2 arecut into the zone. If the oil shale zone is relatively shallow,these'points can be substantially near the top and bottom of the zone,respectively. A short communication lateral 3 is formed in the zone at apoint above tunnel 2 and a cavity 4 is excavated at a point in the zoneintermediate access means 1 and 2 but generally in proximity to one orthe other of the access means. Any of a number of conventional methodscan be used to form the cavity such as by drilling. A communicating holeor pattern of holes 5 is formed from the other of said access means tothe cavity 4. The hole (or holes) 5 is loaded with explosive anddetonated in such a manner as to result in a chimney 6 filled withfragmented oil shale indicated generally as b in FIG. 1c. The mass offragmented oil shale b is a porous mass. Heating means can then besupplied through one 'of the access means to heat the fragmented oilshale to pyrolyze the oil contained therein. The pyrolyzed oil can thenbe collected by means located in or attached to the other access means.The heating means can be, for example, a heated gas, which can benoncombustion supporting, such as natural gas or a mixture of naturalgas and up to about 20 volume percent carbon dioxide, or it can becombustion supporting, such as oxygen or air. The gas can further be amixture of natural gas and air. A combustion supporting gas ispreferred, such as air or a mixture of natural gas and air. Inoperation, it is preferred that the fragmented mass of oil shale besubjected to retorting at a temperature of from about 500 to 1,200 F. todrive off the oil contained therein, followed by a substantiallycomplete combustion of shale. The spent shale can then be treated withan alkaline solution, at atemperature of up to about 220 F. to dissolveany aluminum values present, as in dawsonite, without substantialprecipitation of SiO: and the aluminum values can be recovered from thealkaline solution. The leaching and recovery steps are more fullyexplained in U.S. Pat. application Ser. No. 571,649, filed Aug. 10,1966, now US. Pat. No. 3,5 [6,787.

HO. 2 shows another embodiment of this invention in which two contiguouszones or two contiguous chimneys in one zone are treated simultaneouslyalthough the operation in each zone or chimney at any given moment maybe somewhat different as is explained more fully below. Chimneys 6' and6 contain porous masses of fragmented oil shale indicated as b' and b,formed as porous mass 6 explained above. Air from compressor 7 flowsthrough headworks 8 which contain an ignition system and is ignitedtherein. The air then flows through the shale mass to offtake duct 9 tothe oil recovery system 10, which can be any known oil separationsystem. The oil contained in the shale is retorted during the airflowand also flows into oil recovery system 10. Preferably, the gas 11 whichhas been denuded of oil in recovery system 110 is returned, mixed withair from compressor 13 and is passed to the bottom of the second chimney6". The gas 11 contains primarily combustion products from the airburning and the other noncombustible air compounds. The gas-air mixtureis ignited at the bottom of the chimney and preheats the shale mass inchimney 6" in its passage therethrough to a temperature of about 200 to400 F. The mixture of combustion products and recycle gas passes outthrough headworks l4 and recycle compressor 15 and can be combined withthe air in the headworks 8. The recycle gas has the effect of recoveringheat from the spent shale indicated as 16 above the combustion zone 17,of reducing peak temperature in the combustion zone to minimize fusionand clinkering and of increasing the length of the zone above any giventemperature up to the maximum.

This control of temperature and time is especially useful in convertingminerals which may be contained in the shale oil such as dawsonite to asoluble for ultimate recovery as is more fully explained in theaforesaid copending application Ser. No. 571,649, now U.S. Pat. No.3,516,787.

When the oil shale in chimney 6 is completely retorted and thecombustion zone reaches the bottom of the chimney, air injection can beceased and an inert gas injected to quench burning. Suitable connectionscan be made to start ignition in chimney 6" thus beginning retortingwhile another contiguous chimney (not shown) can be preheated in thesame manner as has been previously described.

This invention may be applied in many ways. in very thick oil shalessections there may be zones which are rich enough for profitable miningand above ground retorting. Such a zone would provide a natural accessto the top or bottom of a section in which chimneys are to be developed.Thus, the process of the instant invention can be combined with a knownabove ground retorting process. In sections of lean shale which are toothick to be retorted in a single chimney without the shapes of thechimney, three access tunnels can be originally formed and chimneysdeveloped above and below the middle tunnel.

FIG. 3 illustrates an embodiment of the instant invention in which achimney of great height can be developed in sections with choke points18 left in the oil shale structure. At this smaller opening on chokepoint 18 the oil shale will bridge the opening as it is fragmented andlimit the static load of the broken shale at any point in the chimneywhile still allowing a steady flow of gas and oil. The communicationtunnels and drifts, although shown essentially round, can have manyshapes.

The advantage of the process is that a large proportion of the oil shalein a given section or bed can be pyrolyzed in situ. This can be done ata fraction of the usual costs per ton for mining, hauling, crushing,handling to retort and spent shale disposal, investment in supply,ignition and recovery systems of the usual above ground retorting plant.The invention is further advantageous for processing leaner shales,operating in areas where disposal and other such problems would precludesurface or subsurface mining and utility and/or more efficiency in areasprecluded for other in situ methods.

Also, if mineral dawsonite exists in the oil shale, it will be convertedto soluble form by the temperatures of retorting and combustion. Thus,after retorting is completed, water or special solutions may be injectedinto the chimney to leach out the aluminum salt and soluble sodium saltsas is more fully explained in the aforesaid Ser. No. 571,649. The liquorfrom this operation would be sent to recovery systems designed for thispurpose.

While the process described herein has been directed particularly to therecovery of shale oil from oil shale, the present invention may beadopted for the recovery of oil from any subterranean oil-containing oroil-producing solid substance. Accordingly, it is to be understood thatthe above description is merely illustrative of preferred embodiments ofthe invention, of which many variations may be made within the scope ofthe following claims without departing from the spirit thereof.

The embodiments of the invention in which I claim an exclusive propertyor privilege are defined as follows:

1. A method of obtaining shale oil from a zone of unmined oil shalewhich comprises establishing access means at at least two points in saidzone, establishing communication between these access means through thezone, fragmenting at least part of the oil shale in the zone in the areaof the communication to produce a porous mass of fragmented oil shale,supplying heating means to said fragmented oil shale through one of saidaccess points to pyrolyze shale oil in the oil shale and collecting saidshale oil through the other of said access means.

2. The method of claim 1 wherein the establishing of communicationbetween said access means includes establishing a cavity in the zoneintermediate the access means and proximate to one of said access meansin which it is in communication and establishing communication betweensaid cavity and the other of said access means.

3. The method of claim 1 wherein said fragmenting is performed usingexplosives.

4. The method of claim 1 wherein the heating means is a gas.

5. The method of claim 4 wherein a second porous mass of fragmented oilshale is formed in another area of communication contiguous to the firstporous mass and the gas from the first mass is transferred through thesecond porous mass to thereby preheat the second porous mass.

6. The method of claim 5 wherein the first porous mass is heated to aretorting temperature of from about 500 F. to 1,200 F. and the secondporous mass is preheated to a temperature of from about 200 to 400 F.

7. The method of claim 1 wherein the oil shale in the zone is fragmentedwith two porous masses in the area of the communication separated by anunfragmented area of the communication.

8. The method of claim 1 wherein the pyrolyzed oil shale is treated withan aqueous solution to recover soluble mineral values contained in thepyrolyzed shale.

9. The method of claim 8 wherein the mineral values include quartz,dolomite and dawsonite, the aqueous solution is an alkaline solution,and the pyrolyzed shale is treated with the alkaline solution at atemperature of up to about 220 F. to dissolve aluminum values in saiddawsonite without substantial precipitation of SiO,.

2. The method of claim 1 wherein the establishing of communicationbetween said access means includes establishing a cavity in the zoneintermediate the access means and proximate to one of said access meaNsin which it is in communication and establishing communication betweensaid cavity and the other of said access means.
 3. The method of claim 1wherein said fragmenting is performed using explosives.
 4. The method ofclaim 1 wherein the heating means is a gas.
 5. The method of claim 4wherein a second porous mass of fragmented oil shale is formed inanother area of communication contiguous to the first porous mass andthe gas from the first mass is transferred through the second porousmass to thereby preheat the second porous mass.
 6. The method of claim 5wherein the first porous mass is heated to a retorting temperature offrom about 500* F. to 1,200* F. and the second porous mass is preheatedto a temperature of from about 200* to 400* F.
 7. The method of claim 1wherein the oil shale in the zone is fragmented with two porous massesin the area of the communication separated by an unfragmented area ofthe communication.
 8. The method of claim 1 wherein the pyrolyzed oilshale is treated with an aqueous solution to recover soluble mineralvalues contained in the pyrolyzed shale.
 9. The method of claim 8wherein the mineral values include quartz, dolomite and dawsonite, theaqueous solution is an alkaline solution, and the pyrolyzed shale istreated with the alkaline solution at a temperature of up to about 220*F. to dissolve aluminum values in said dawsonite without substantialprecipitation of SiO2.